The proposed studies are designed to investigate some of the fundamental interactions which occur between cortical neurons and applied electric fields. A stimulating electrode located either intracortically or on the surface of the cat visual cortex is used to deliver capacitance-coupled pulses of constant current. A nearby recording microelectrode measures the response of cortical neurons close to the site of neural stimulation. The latency of response and the threshold current for neuronal activation is measured for a population of neurons in the vicinity of the stimulating electrode. Neurons activated by cortical stimulation are classified according to their receptive field characteristics. Both extracellular and intracellular studies of cortical neurons are carried out.